covalent contribution in bonds

orb overlap (wavefunctions)

ionic contribution in bonds

attraction from opposite charges

what type of bonds make up main group organometallics?

largely M-C σ bonds of various strengths and polarity

9

electronegativity of element increases with

higher oxidation state eg Ti(IV) > Ti(I)

10

is electronegativity of element such as carbon constant?

no- depends on the amount of s-contribution to hybrid orbs (s-orb more strongly affected by effective nuclear charge than other orbs) the more s character, the more electronegatiive and the stronger the M-C bond strength

11

polarity trends in main group organometallics

1. M-C bond polarity decreases from left to right in table 2. M-C bond polarity increases down a group

12

bond strength trends in main group organometallics

decreases down a group

13

what does mean bond energy do going a group and why?

energy decreases due to different radical expansion and poorer orb overlap for heavier metals and period 2 elements eg carbon

14

are organometallic compounds stable/unstable with respect to oxidation to MOn, CO2, H2O

organometallic compounds are thermodynamically unstable

15

generally what types of organometallics are reactive towards air and moisture?

(MeAlO)n, can come in polymer chains, rings or cages synthesised from hydrolysis of waterused to activate catalysts eg in Zieglar-Natta polymerisation

Role of MAO during polumerisation

Tebbe Reagent

Cp2Ti- (CH2, Cl) bridge- AlMe2

76

use of Tebbe reagent

can be used to transfer a methylene to a ketone - replaces double bond O

77

Group 14 organometallics ER4

1. stable - not e- deficient 2. less reactive/nucleophilic due to low bond polarity of E-C 3. E-C bond strength decreases down the groupE-C bond polarity decreases down the group 4.thermal stability of ER4 decreases down the group